The invention concerns a drill string element and a drill string composed of such elements.
Elements of that type are used in the field of drilling, in particular drilling for oil, to form a drill string which extends from the surface of the well to the bottom thereof.
Those elements comprise in particular the drill pipes, the heavy drill pipes and the drill collars. The specifications of the American Petroleum Institute (or ‘API’) define for example such elements.
In the course of the drilling operation new elements are connected in butting relationship to the elements already present in the drill string to extend the latter and to continue drilling to a greater depth.
At the present time measurement devices are disposed in the drill string to measure certain physical parameters relating to the drilling well, its environment or the drill string itself. Those devices which can be of varying types are in particular disposed in the proximity of the lower end of the drill string.
Memory systems can in some cases be associated with the measurement devices to record the measurement results.
Electrical energy is necessary for operation of the measurement devices and the memory systems.
Conventionally, electric batteries and/or turbine-type power generators are therefore added to the measurement devices. If necessary the turbine is caused to rotate by the flow of drilling fluid circulating through the elements of the drill string.
On the other hand it is appropriate for the measurement results attained to be communicated to the surface of the drilling well, without the whole of the drill string being pulled up to the surface.
To do that telemetry devices can be used, which are disposed in the well. For example electromagnetic devices operating at very low frequency can be used.
It is also possible to modulate the flow of the drilling fluid circulating in the interior of the drill string so that variations in the pressure and/or flow rate thereof can be detected at the surface.
The conventional devices both for the supply of electrical energy and for taking up the measurement data suffer from many different well-known disadvantages which involve in particular resistance to the loads encountered and the complexity in terms of connection of the different elements together along the drill string, and each time a fresh element is joined to the structure.
Finally a simple way of transporting electrical power and the measurement signals is to use electrically conductive elements of fixed-wire type. Different arrangements have thus been proposed for accommodating those conductor elements in the drill string elements.
Those arrangements however must meet certain demands such as for example reversible and easy connection of the elements together, resistance to the torsional, bending, compressive or tensile loads, unexpected shocks and vibrations or also erosion by the drilling fluid.